This invention relates to a real-time simulation system for testing controllers of Anti-Skid Brake Systems (hereinafter referred to as ABS), and in particular to a real-time simulator capable of simulating a moving car by employing a personal computer which sends a set of car dynamic data to the ABS controller which in return feeds control signals back to the personal computer. The personal computer calculates and analyses the control signals and displays the results on its monitor.
Most car drivers believe that they can fully stop a car in a short distance if they fully depress the brake-pedal. However, many experiments have shown that, although fully depressing the brake-pedal applies a large braking torque to the car wheels, large braking torque can cause the car wheels to lock. This locking of the car wheels inevitably causes skidding of the tires and spinning of the car and the subsequent loss of control which often results in accidents.
While the car wheels skid on the road and spinning of the car occurs when the wheels are locked during braking if the car wheels continue to roll on the road during braking with slip ratio around 0.1 to 0.3, quasi static friction occurs between the car wheels and the road. This is due to the fact that the point of the car wheel which contacts the ground stays still relative to the ground at the instant of contact. In other words, the car wheels continue to roll (rather than skid) during braking. As people skilled in this art know, dynamic friction coefficients are smaller than static friction coefficients. Thus, keeping the wheels of a car rolling during braking will result in larger frictional forces between the car wheels and the road. Furthermore, if car wheels keep rolling during braking, the car tends to move in the direction of the rolling wheels, and the driver is thus capable of maintaining control of the car in his/her own way during braking. However, if the car wheels lock during braking, the wheels will slip and the car will not have as strong a tendency to continue in the original direction of the wheels. Thus, the car will spin out of control. Therefore, more and more cars are equipped with ABS which are provided with sensors for sensing tire speeds and inputting the speed data into a CPU installed within the system so as to assist the driver in preserving braking control.
There are presently many patents relating to this kind of simulator, for example, U.S. Pat. Nos. 4,831,868, 4,893,242, 4,926,683, and 4,986,114. Among the above-described patents, the '868 patent proposes to employ a tester coupled to an ABS controller. The tester outputs a command actuating the ABS controller to work in a testing mode and tests the ABS controller by transmitting signals between the ABS controller and the tester. The '242 patent proposes a method in which car wheels are driven to accelerate to a certain constant speed by a motor, then the brake-pedal is depressed linearly so as to measure the brake torques imposed on each car wheel. The '683 patent proposes to check whether each wheel sensor outputs signals normally or not when the speed of the car wheels are kept at the minimum speed controlled by a controller. If one of the car wheels fails to output signals, a warning lamp will keep glowing. The '114 patent proposes a method in which car wheels are driven to accelerate by a drive roller so as to simulate the dynamic properties of a brake system on different roads.
The above-described systems are either too complicated in actual operation or cannot produce precise results. When maintenance of a controller is necessary, only some simple diagnostic devices are provided by manufacturers for maintaining their own controllers. These devices are merely employed to read error-condition codes from the controllers so as to determine how to maintain the controller. For training in the principles of braking systems, a testing device provided with a brake mechanism is ordinarily employed. The comparison between an ABS and a conventional brake system can be illustrated through the testing device, and some particular situations can also be simulated through the testing device. However, the principles of an ABS cannot be illustrated by utilizing the above testing device.